Many laboratory and clinical procedures involve processing a sample to separate a target from the sample for subsequent identification and analysis of the target. Such processes are commonly used to detect a wide range of targets, including biological entities such as cells, viruses, proteins, bacterium, nucleic acids, etc., and have applications in clinical diagnostics, biohazard screenings, and forensic analyses.
Often there is an immediate need to identify the target, whether to determine the proper course of treatment or to develop response protocol for biohazard threat. For example, blood-borne pathogens are a significant healthcare problem because a delayed or improper diagnosis can lead to sepsis. Sepsis, a severe inflammatory response to infection, is a leading cause of death in the United States and early detection of the blood-borne pathogens underlying the infection is crucial to preventing the onset of sepsis. With early detection, the pathogen's drug/antibiotic resistant profile can be obtained which allows the clinician to determine the appropriate anti-microbial therapy for a quicker and more effective treatment.
Pathogens during active blood-borne infection or after antibiotic treatment are typically present in minute levels per mL of body fluid. Several techniques have been developed for isolation of pathogens in a body fluid sample, which include molecular detection methods, antigen detection methods, and metabolite detection methods. These conventional methods often require culturing specimens, such as performing an incubation or enrichment step, in order to detect the low levels of pathogens. The incubation/enrichment period is intended to allow for the growth of bacteria and an increase in bacterial cell numbers to more readily aid in isolation and identification. In many cases, a series of two or three separate incubations is needed to isolate the target bacteria. Moreover, enrichment steps require a significant amount of time and can potentially compromise test sensitivity by killing some of the cells sought to be measured. In certain cases, a full week may be necessary to reach the desired levels of bacteria.
The above techniques can be carried out on microfluidic devices to separate the pathogen or target from the sample. However, current microfluidic devices require extensive sample preparation prior to introducing the sample into the device for subsequent isolation. Microfluidic devices by definition are designed to conduct reactions and process at a microfluidic scale. To isolate pathogens in a microfluidic device, it is necessary to incubate/enrich the sample to expand the levels of pathogens to increase the chance that the small volume of sample introduced into the microfluidic device contains a pathogen. Alternatively, a large volume of fluid suspected of containing a pathogen is introduced at an extremely slow pace through a tube or by piecemeal pipetting the sample into the microfluidic device. These methods are equally time consuming as incubation and can result in loss of clinically relevant sample (i.e. sample with sufficient levels of targets for capture). In addition, the transfer of large volume of fluid into the microfluidic device may expose the sample to contamination.
Currently, there is no effective device capable of rapidly and effectively isolating a target that is fast and sensitive in order to provide data critical for patient treatment and biohazard analysis in a clinically relevant time frame.